This invention relates to triple-stranded nucleic acids.
Such nucleic acids have been observed in which a central polyadenylate (poly(A)) strand is hydrogen bonded to two polyridylate (poly(U)) strands (e.g., Felsenfeld et al., 26 Blochim. Biophys. Acta. 457 (1957)). This triple-stranded structure has been described by Arnott et al., 244 Nature New Bio. 99 (1973), as having one poly(U) strand hydrogen bonded to the poly(A) strand in the Watson-Crick manner, and the second poly(U) strand hydrogen bonded to the poly(A) strand in a Hoogsteen-type arrangement, with the second poly(U) chain being oriented parallel to the poly(A) strand. Watson-Crick manner, as used herein, means the standard hydrogen bonding arrangement that is present in double-stranded nucleic acids (A.multidot.T/U, G.multidot.C).
Howard et al., 246 J. Biol. Chem. 7033 (1971), describe a triple-stranded nucleic acid having a central polydeoxyadenylate (poly(dA)) strand hydrogen bonded to two polydeoxythymidylate (poly(dT)) strands. Arnott et al., 3 Nuc. Acid Res. 2459 (1976), say that both this structure and poly(U).multidot.poly(A).multidot.poly(U) exist as A-type helices.
Other triple-stranded nucleic acids that have been reported include a central polyguanylate (poly(G)) strand hydrogen bonded to two polycytidylate (poly(C)) strands (Lipsett, 239 J. Biol. Chem. 1256 (1964)); a central poly(G) strand hydrogen bonded to a poly(C) strand and a second poly(G) strand (Fresco, in Informational Macromolecules: A Symposium. 121 (1963)); a central polyinosinate (poly(I)) strand hydrogen bonded to two poly(C) strands (Arnott et al., 3 Nuc. Acid Res. 2459 (1976)); and a-central poly(dA-dG) strand (in which deoxyadenosine and deoxyguanosine residues alternate) hydrogen bonded to a poly(dT-dC)-strand (in which deoxythymidine and deoxycytidine residues alternate) and a poly(U-C) strand (in which uridine and cytidine residues alternate) (Morgan et al., 37 J. Mol. Bio. 63 (1968)).